In principle, photometric analysis is a method for determining the quantity of elements in a sample solution in which the solution color is affected and by the elements specific wave lengths are measured.
Since photometric analysis has great advantages over other wet chemical analysis with respect to sensitivity, selectivity, rapidity, etc., much research for analysis methods has been attempted for various kinds of samples.
However, conducting these analyses is complicated and troublesome, requiring much time and expert techniques. The photometric analysis method may be roughly classified into following five unit steps or operations. These operations are:
1. Preliminary treating of sample solution, PA1 2. Adding coloring solutions, PA1 3. Coloration, PA1 4. Measuring for absorbancy and PA1 5. Measuring for a blank value.
In some cases, one or two of the above operations may be omitted, but, in principle, the operations are carried out in the above mentioned order. Quantitative analysis of the elements is calculated from prepared calibration curves.
In case of a solid sample, a dissolving operation is added prior to the operation (1), so that when the solution sample, which is a solution of the solid sample, is used as a starting substance, the operations are the same.
There are two typical types of automatic photometric analysers on the market. One operates as follows: a sample solution and coloring solution are continuously fed by means of a pump, coloring reactions occur in a feed pipe and at the end portion of feed pipe, apparatus is located for continuously measuring the absorbancy. The other type operates as follows: A number of test tubes are successively moved, and a sample solution and coloring solution are successively injected into the test tubes by means of an injection type pump to carry out color reaction. Thus the test tubes are then used as cells for measuring the absorbancy, and the absorbancy of solution in the test tubes may be continuously measured.
However, with regard to simplicity, low cost, precision and accuracy of analysis, these types of apparatus are not sufficient for practical use.